The present invention relates in general to motor vehicle suspension systems which include controllable ride height, for example by an air suspension control system, and, more particularly, to ride height control for vehicles having manually and/or automatically selectable drive wheels including at least a two wheel drive setting and a four wheel drive setting.
Motor vehicle suspension systems are connected between the body of the vehicle and the wheels to determine the ride and handling of the vehicle. Conventional suspension systems include springs and shock absorbers which are typically fixed such that the ride and handling are fixed and the level of the vehicle depends upon the loading of the vehicle.
More advanced suspension systems include controllable elements such as variable damping shock absorbers which permit a number of damping factors to be selected as needed. Controllable springs may also be included. Such springs are typically pneumatically or air controlled and are inflated to increase the spring rate of the overall vehicle spring system and deflated to decrease the spring rate. Vehicle suspensions including controllable springs may be electronically controlled to select vehicle ride height relative to the wheels or ground based on the speed of the vehicle. Ride height can therefor be reduced to reduce drag and increase efficient operation at highway speeds and raised to increase clearance at lower speeds and for convenient entry and exit from the vehicle when stopped.
Unfortunately, for vehicles which include automatic and/or manual drive wheel selection including at least a two wheel drive setting and a four wheel drive setting, vehicle height selection based on speed is not entirely satisfactory. It is, thus, apparent that there is a need for an improved suspension control system to better select ride height settings for such vehicles.